PASADENA, Calif. -- The Martian arctic soil that NASA's Phoenix Mars Lander dug into this year is very cold and very dry. However, when long-term climate cycles make the site warmer, the soil may get moist enough to modify the chemistry, producing effects that persist through the colder times.

Phoenix found clues increasing scientists' confidence in predictive models about water vapor moving through the soil between the atmosphere and subsurface water-ice. The models predict the vapor flow can wet the soil when the tilt of Mars' axis, the obliquity, is greater than it is now....Cloddy texture of soil scooped up by Phoenix is one clue to effects of water. The mission's microscopic examination of the soil shows individual particles characteristic of windblown dust and sand, but clods of the soil hold together more cohesively than expected for unaltered dust and sand. Arvidson said, "It's not strongly cemented. It would break up in your hand, but the cloddiness tells us that something is taking the windblown material and mildly cementing it."

That cementing effect could result from water molecules adhering to the surfaces of soil particles. Or it could be from water mobilizing and redepositing salts that Phoenix identified in the soil, such as magnesium perchlorate and calcium carbonate.

The Thermal and Electrical Conductivity Probe on Phoenix detected electrical-property changes consistent with accumulation of water molecules on surfaces of soil grains during daily cycles of water vapor moving through the soil, reported Aaron Zent of NASA Ames Research Center, Moffett Field, Calif., lead scientist for that probe.

"There's exchange between the atmosphere and the subsurface ice," Zent said. "A film of water molecules accumulates on the surfaces of mineral particles. It's not enough right now to transform the chemistry, but the measurements are providing verification that these molecular films are occurring when you would expect them to, and this gives us more confidence in predicting the way they would behave in other parts of the obliquity cycles."

The Thermal and Electrical Conductivity Probe on Phoenix detected electrical-property changes consistent with accumulation of water molecules on surfaces of soil grains during daily cycles of water vapor moving through the soil, reported Aaron Zent of NASA Ames Research Center, Moffett Field, Calif., lead scientist for that probe.

Is this a complete turnaround from previous reports, or did I miss something?

"For example, they saw a low-temperature release of carbon dioxide (CO2). This could be a number of things: iron or magnesium carbonates; adsorbed carbon dioxide; or potentially most exciting, combusted organics."

"...if there were organics present, they could have been destroyed by the perchlorate during heating before TEGA had a chance to detect them. Unfortunate --..."

Why cannot the calorimeter distinguish between these possibilities? Wouldn't combusted organics be signalled by an exothermic process? Whereas the others would be endothermic, right?

I think it's consistent. They saw vapour, they saw films, but they didn't see liquid - I think is the main story.

Doug

I'm going to be hopelessly pedantic here Doug: the report describes that

QUOTE

"A film of water molecules accumulates on the surfaces of mineral particles. It's not enough right now to transform the chemistry, but the measurements are providing verification that these molecular films are occurring when you would expect them to, and this gives us more confidence in predicting the way they would behave in other parts of the obliquity cycles."

"There are no indications of thin films of moisture, and this is puzzling.....the probe can detect films of water barely more than one molecule thick."

If the films were around the one molecule thick mark, or the electrical characteristics of the soil were different than expected, or any one of a zillion things, I totally get that the readings might have needed carefully examining before the evidence was apparent. I'm just wondering how exactly they got from 'the soil is puzzlingly free of water', to 'the soil has some thin films of water molecules'.

I agree, Marsbug - I also noticed that change in the interpretation of the results and I'm curious about the details too.

If you haven't noticed it, a plot of "simplified" data from TECP was presented yesterday. Perhaps this gives us a clue. To my eye there's no clear anticorrelation between the atmospheric and soil measurements - there are peaks in the soil measurement during the day. Perhaps a sign that there's some non-trivial dynamics going on here - more than just a simple "soil at night" and "air during the day" cycle?

I wouldn't describe it as "hopelessly pedantic", just being curious about the scientific process...

Wow, thanks for the cool graph fredk; I am sure my temporal insomnia and headache last night was because of this subject (to detect or not to detect water film, that *was* the bloody question!). The graph clearly shows that the ice is literally breathing. Cool.

If you haven't noticed it, a plot of "simplified" data from TECP was presented yesterday. Perhaps this gives us a clue. To my eye there's no clear anticorrelation between the atmospheric and soil measurements - there are peaks in the soil measurement during the day. Perhaps a sign that there's some non-trivial dynamics going on here - more than just a simple "soil at night" and "air during the day" cycle?

Well we have a layer of ice, lying below a fairly complex regolith mixture containing water absorbing salts, as well as grains for water molecules to adhere to, and probably a small amount of ice in some form, topped by water/CO2 frosts and snow coming from an atmosphere that supports water ice clouds. So there's a lot of sinks and sources of water, which means complex behavoir for water in the soils is pretty inevitable.

On the subject of the films, the impression I get on re-reading the release and the articles is that the team are probably being a little cagey because there's still a lot of analysis ahead. My hunch is that the films are probably averaging less than one molecule thick throughout most of the soil, and hence form as a series of patchy 'islands' around favourable spots for water molecules to deposit. That would make them much harder to 'see' as a continous electrical path through the soil wouldn't be there. So when the team digs into the data they may find evidence for these islands of water activity, but hesitate to describe them as films, because....er.... well they aren't they're little islands of H2O clustered together!

Thanks! I've had a quick look, but I've not found anything relating to the growth of thin water films under matian pressures and temperatures, although this and this might have some interest for anyone with access to springer link.I think it's an experiment someone will be doing at some point in the near future though!

It's a little known fact that there were three brothers, Ienstein, Einstien, and Einstein. Albert was actually their family name (the family had Asian roots). The first two shared the limelight, taking alternate holidays, to preserve some privacy for the family. Albert Ienstein is a character best left unremarked upon....

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted.
Do not reproduce without permission. Read
here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the
individual posters and do not necessarily reflect the opinions
of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer
UnmannedSpaceflight.com moderation team is wholly independent
of The Planetary Society. The Planetary Society has no influence
over decisions made by the UnmannedSpaceflight.com moderators.

SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society
and is funded by donations from visitors and members. Help keep
this forum up and running by contributing
here.